The present invention relates in general to the determination of physical properties of materials. More particularly, the present invention relates to an apparatus, program product and method of estimating the stress intensity factor ratio (SIFR) of a material.
The development of the EDVAC computer system of 1948 is often cited as the beginning of the computer era. Since that time, computer systems have evolved into extremely sophisticated devices, and computer systems may be found in many different environments. Since the dawn of the computer age, the performance of computers has been measured to determine how well the computer performs certain tasks. One measure of computer performance is reliability, availability and serviceability (RAS). The physical properties of materials used in, or contemplated for use in, components of computer systems are often evaluated to increase the RAS of the computer systems. For example, computer systems typically contain numerous electronic circuit boards, such as a multi-layered electronic backplane. A thermal or mechanical failure of a material used in the electronic circuit board can decrease the RAS of the computer system in which the board is installed.
Consequently, materials used in, or contemplated for use in, components of computer systems are typically subjected to testing mechanisms to evaluate their physical properties such as fracture toughness, i.e., an inherent material property which describes the resistance to a fracture. For example, a hardness tester may be employed to evaluate a material""s fracture toughness. A hardness tester subjects the component to a load. Typically, the load is increased until the component fractures. This testing mechanism is undesirable for a number of reasons. Firstly, hardness testers typically subject the component to a destructive test. Components such as multi-layered electronic backplanes are relatively costly and their destruction adds to the cost of computer systems. Secondly, hardness testers typically do not provide the stress intensity factor ratio (SIFR) of the material under evaluation. The SIFR is the ratio of a shear (mode 2) stress intensity factor K2 over a normal (mode 1) stress intensity factor K1 (SIFR=K2/K1). Knowledge of the SIFR is advantageous in the evaluation of the material, e.g., knowledge of the SIFR allows calculation of the stress level. However, the SIFR is typically not provided by hardness testers at least in part because of the relative complexity of the measurements and calculations heretofore necessary for its generation.
Therefore, there exists a need to provide an enhanced testing mechanism that readily provides the SIFR of a material under evaluation. There also exists the need for such an enhanced testing mechanism that is preferably non-destructive to the material under evaluation.
An object of the present invention is to provide an enhanced material testing mechanism that addresses these and other problems associated with the prior art.
These and other objects of the present invention are achieved by providing an apparatus, program product, and method for estimating the stress intensity factor ratio (SIFR) of a material. The material is supported on a support and a load is applied to the material using a load member. A pair of strain components are measured using a strain gage attached to the material, and are stored in memory. The strain gage may be a rosette strain gage, for example. A processor calculates a ratio of the stored pair of strain components to thereby provide an estimate of the SIFR of the material. Advantageously, this estimate of the SIFR of the material is readily provided. Also advantageously, the estimate may be provided in a manner that is non-destructive to the material.
In one case, the pair of strain components in a polar coordinate system are radial strain xcex5rr and axial strain xcex5xcex8xcex8, and the ratio of the pair of strain components is xcex5rr/xcex5xcex8xcex8. In an alternative case, the pair of strain components in a Cartesian coordinate system are shear strain xcex5xy and normal strain xcex5yy, and the ratio of the pair of strain components is xcex5xy/xcex5yy 
The processor may additionally calculate the stress level of the material based on the estimated SIFR. The stress level of the material may be calculated as "sgr"=SIFR (xcex5E), "sgr" being the stress level of the material, SIFR being the estimated stress intensity factor ratio, xcex5 being the strain of the material, and E being Young""s modulus of the material.